In interlacing, the pictures forming the video are captured at two distinct time intervals. The pictures forming the video comprise a plurality of ordered lines. During one of the time intervals, video content for the even-numbered lines is captured. During the other time interval, video content for the odd-numbered lines is captured. The even-numbered lines are collectively known as the top field, while the odd-numbered lines are collectively known as the bottom field.
On an interlaced display, the even-numbered lines are displayed on the even-numbered lines of the display during one time interval, while the odd-numbered lines are displayed on the odd-numbered lines of the display during another time interval.
With progressive displays, however, all of the lines of the display are displayed at one time interval. As noted above, the interlaced video pictures include even-numbered lines captured at one time interval, and odd-numbered lines captured at a second time interval. The deinterlacing process generates pictures for display during a single time interval from the interlaced video.
Deinterlacing by combining content from adjacent fields (known as weaving) is suitable for regions of the picture that are characterized by less object motion or lighting changes (known as inter-field motion). Displaying both the top field and bottom field at the same time interval can be problematic in cases where the video content with high-speed motion or lighting changes. Objects that are in motion are at one position when the top field is captured and another position when the bottom field is captured. If the top field and the bottom field are displayed together, a comb-like, or jagged edge affect will appear with the object. This is referred to as an artifact.
Alternatively, deinterlacers can generate a picture for progressive display by interpolating missing lines in a field from adjacent and surrounding lines. This is known as spatial interpolation, or “bobbing”. While spatial interpolation avoids artifacts in regions with high inter-field motion, spatial interpolation loses vertical detail and results in a blurry picture.
Median based deinterlacers use median tests to detect motion for each interpolated pixel. For example, where A and B denote the pixels directly above and below the interpolated pixel in the current field, and where C is the pixel in the exact spatial location in the complimentary field, median interlacers examine the median of A, B, and C. Where the median is C, the median based deinterlacers deduce a monotonic pixel gradient. The monotonic gradient is unlikely if the interpolated pixel and C are part of a moving object. Thus, the median based deinterlacers set the interpolated pixel to C. Where the median is not equal to C, median based deinterlacers set the interpolated pixel to the average of A and B.
The median test can be performed either independently for luma and chroma pixels. Alternatively, a median based deinterlacer can perform the median test on just the luma pixels and use the results to update both the luma and chroma components. Median based algorithms use three lines of storage and simple comparators with integer averaging.
However, the foregoing can introduce some unpleasant artifacts. At the edge of a moving object a hard transition is made from pixel copying to pixel averaging. Due to unequal object motion between fields and due to noise, the exact location of this transition is not constant. A pixel on the edge, which was spatially averaged in one field, could be simply copied in the next field and vice versa. This causes a buzzing flicker artifact along the edge. Additionally, the averaging function of vertically adjacent pixel implicitly assumes that the pixel gradients are vertically oriented. This is not always true at object edges where the gradients are oriented along the object's edge. This can cause a stair step pattern pixel reconstruction.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.